One type of semiconductor package is known as a lead-on-chip (LOC) package. A lead-on-chip package includes a semiconductor die encapsulated in a polymeric material (e.g., epoxy resin). This package is formed using a metal leadframe. The leadframe supports several dice for packaging and provides the leads for the completed package. A conventional leadframe includes a mounting paddle for each die and lead fingers that are wire bonded to bond pads on the die and then trimmed and formed into leads. However, with a lead-on-chip package, the lead fingers of the leadframe, not only form the leads in the completed package, but also support the die during the encapsulation process.
Prior to the encapsulation process, the die is attached to an underside of the lead fingers. The LOC package provides superior heat transfer from the die and shortens the length of the bond wires. In addition, the LOC package can be formed with a more reliable seal. U.S. Pat. No. 4,862,245 to Pashby et al. and U.S. Pat. No. 4,916,519 to Ward describe lead-on-chip semiconductor packages.
A common method of attaching and wire bonding a LOC die to a LOC leadframe is known as area wire bonding, or A-wire bonding. A conventional A-wire bonding process begins by attaching the die to the lead fingers of the leadframe. For attaching the die to the leadframe, a double-sided adhesive tape can be used. The tape includes a thermoset adhesive on both sides such as an epoxy, acrylic, silicone or polyimide. This type of tape is sometimes referred to as LOC tape and can also function as an alpha barrier for the die. The LOC tape is initially attached to the leadframe using heat and pressure. Then the face of the die is attached to the LOC tape using heat and pressure and an oven is used to cure the adhesive. After the curing step, the leadframe is transferred to a wirebonder machine where bond wires are attached to the bond pads of the die and to the lead fingers of the leadframe.
Prior to the die attach, the LOC tape must be placed onto the heated leadframe in a configuration that secures the die to the lead fingers but allows access to the bond pads of the die for wirebonding. Typically, a single piece of LOC tape is dispensed from a continuous roll of tape and then punched into two decals that are spaced apart and cut away to provide access to the bond pads.
One problem with this process is that LOC tape is an expensive material and a large amount of tape is wasted during formation of the LOC decals. With a conventional LOC punching apparatus the width of the tape must be large enough to punch two decals with a space in-between the decals. Typically, the decals are punched from the center of a continuous length of tape having a width that is much larger than the peripheral dimensions of the decal. In addition, there is wasted tape across the length of the tape in an area between the decals for adjacent dice. In some systems approximately 50 to 75% of the tape is wasted. It would be advantageous to be able to form a LOC decal without wasting tape.
In view of the foregoing, it is an object of the present invention to provide an improved method and apparatus for cutting LOC tape into decals and for applying the cut decals to a leadframe with no wasted tape.
It is yet another object of the present invention to provide an improved apparatus for cutting LOC tape and for applying the cut decals to a leadframe at production speeds and with no wasted tape.
Other objects, advantages and capabilities of the present invention will become more apparent as the description proceeds.